Rod-type specimen stage for electron optical instruments



June 6, 1950 Y J. H. REISNER 2,510,349

ROD TYPE SPECIMEN STAGE FOR ELECTRON OPTICAL INSTRUMENTS Filed Nov. 1, 1948 INVENTOR JET-1N I-LREIS ER BY% ATTORNEY Patented June 6, 1950 ROD-TYPE SPECIMEN STAGE FOR ELEC- TRON OPTICAL INSTRUMENTS John H. Reisner, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 1, 1948, Serial No. 57,674

Claims. 1 This invention relates to electron-optical ins'truments, particularly to improvements in the specimen stages of such instruments, and has special reference to improvements in specimen stages of the type (exemplified by U. S. Patent 2,264.210 to Krause) wherein the specimenholder comprises a rod, containing one or more specimen-holding apertures, and which may be entered into and withdrawn from the evacuable interior of the instrument through an elastic bushing without seriously impairing the vacuum within the instrument.

The rod-type of specimen holder as presently used in electron optical instruments has the following advantages, (a) simplicity of construction and (21) its use involves the introduction of the least possible amount of air into the evacuated interior of the instrument when changing specimens. It has the disadvantage, however, of possessing but one freedom of translational motion, i. e. along the axis of the rod. Motion at a right angle to the rod can only be approximated, in orienting the specimen with respect to the electron beam, by rotating the rod about its axis. The degree of exactness with which the specimen may be oriented by rotating the holder about its axis is quite coarse and, in fact, limits the magnification cf the instrument in which a rod-like holder is employed to 10,000 diameters, more or less. Furthermore, in such a holder the specimen must be mounted sufiiciently far from the pole-pieces of the objective lens to permit rotation of the rod without striking any part of the lens. This necessitates the use of a long focal-length lens and such a lens, inherently, has a lower resolution than a short focal length lens.

Accordingly, the principal object of the present invention is to provide an improved specimen stage for electron-optical instruments and one which shall possess the simplicity and vacuumretaining features characteristic of a rod-type specimen holder and, also, the high resolution, high magnification and flexibility heretofore achieved only with electron-optical instruments containing an evacuable auxiliary chamber or air-loo The invention will be described in connection with the accompanying drawing wherein:

' Fig. 1 is a plan view taken on the line I-| of Fig. 2 showing a specimen stage of an electron optical instrument incorporating the invention,

Fig. 2 is a sectional elevation, taken on the line 2 -2 of Fig. l and,

Fig. 3 is an enlarged sectional view of the specimen holder taken on the line 33 of Fig. l.

In the illustrated embodiment of the invention l designates, generally, a hollow metal body or casting which will be understood to form part of the evacuable casing of an electron-microscope, diffraction camera or analogous electron-optical instrument, and :rx (see Fig. 2) designates the optical axis of the instrument along which electrons travel from an electron gun or other source (not shown) to a fluorescent screen, photographic plate or other target (not shown).

The electrons in their journey between the gun and the target pass through the beam-forming aperture 2 in the bottom of an inverted cupshape member 3 and thence through the aligned apertures 4 and 5 in the pole-pieces 6 and I of an electron-lens. The lens here shown is of the permanent magnet type described in copending application Ser. No. 17,846, now Patent No. 2,464,382, of the same inventor, though it may comprise a lens of the electromagnetic type or, indeed, of the electrostatic type. In any event, the upper pole piece 5 of the lens is provided with a preferably p1ane top surface 6a which serves as an immovable pedestal for the cup-shape member 3 and for the flat surface 81) (see Fig. 3) of a movable rod-like specimen holder 8, later described.

The chamber l0 within which the apertured lens elements 3, 6 and i are contained has a base in the form of a plane surface Ilia upon which a short upright cylinder l l is mounted for slideable movement in all directions about the common axis 0:a: of the immovable lens elements, 3, 6 and i. This slideable member H and the cylindrical wall of the immovable cup-shape member 3 are each provided with a pair of oppositely located holes i la, I ib-3a, 3b, respectively, through which the rod 8 extends. It will be observed that the rod 8 has a sliding fit in the holes Ha, III) of the movable cylinder or carriage l I, hence the rod may be moved longitudinally, in either direction on and with respect to the said carriage. The holes 3a and 3b in the immovable cup-shape member 3, on the other hand, are of a diameter substantially greater than that of the rod 8, which is thus free to be moved both longitudinally and laterally within the said holes for the purpose of orienting the specimen-holding aperture So on the said rod 8 with respect to the axis x-x of the electron beam.

The fact that the rod 8 has a flat bearing-surface 8b and is not subject to rotation about its axis permits the specimen to be mounted (as on a fine mesh screen 8s, adjacent to the lower end of the specimen holding aperture 8a) very close to the upper pole-piece 6 of the lens. In agreement with a known law of electron-optics, this makes it possible to use properly energized pole-pieces wherein the ratio of the spacing of the pole-pieces to the diameter of the apertures therein approaches the theoretically optimum ratio (of approximately l.3 to 1) required to achieve a magnified image of the highest possible resolution. (As previously indicated, it is impossible to achieve an electron image of very high resolution in an instrument having a specimen-holder which must be tilted or rotated to bring the specimen into optical alignment with the pole-piece apertures.)

As shown in Fig. l, the rod-like specimen holder 8 extends to the exterior of the instrument through a bore 12 in the wall of the casing l and may be entered into and withdrawn from the lens chamber l through a vacuum-tight elastic bushing It by applying the appropriate axial force to a knob M on the outer end of the rod. The bore l2 which receives the rod 8, and within-which thebushing i3 is mounted, is of a diameter substantially greater than that of 'the rod, so that the rod may be subjected to a lateral .pivotal'movement (about the center of the bushing) when required to bring the specimen-holding aperture 8a into register with the axis a;-a: of thegelectron beam.

It will be observed that the rod is provided with a circumferential groove [5 adjacent to its leading end and with a similar groove l6 intermediate the specimen-holding "aperture 8a and its outer or knob end. These grooves l5 and E6 serve as catches for a latch ll which is mounted on the carriage l! surrounding one of the openings! in through which the rod 8 extends. When thexrod is'withdrawn from the casing a distance suiiicient to permit access to its specimen-holding aperture 8a the latch l'i will engage the groove l5 and effectively prevent the rod from being pulled all the way out and thus breaking the'vacuum within the instrument. On the other hand, when the rod is pushed in to a position Whereat the latch ll engages the other groove or catch E6 the operator will be advised by his sense of touch that the specimen holding aperture 8a is either (a) in register with or (b) in linewith the electron beam or else (0) lies on the arc of a circle which intersects the axis of thebeam. In the later cases, the specimen holding aperture may be moved into register with the beam by subjecting the carriage ll upon which the rod 3 is supported to appropriate linear or curvilinear movement.

The mechanism here shown for imparting the required linear and/or curvilinear movements to the specimen holding rod 8 through its carriage I! comprises two spring actuated plungers 2! and 2! mounted 90 apart in the inner wall of the-casing i on opposite sides of the rod 8 and two threaded plungers 22, 23 similarly arranged, and which extend through suitable vacuum tight bushings 2c and 25 to the exterior of the casing where they terminate in control knobs 26 and 21. .It will be observed that the outer surface of the cylinder or carriage l to, which the plungers are presented is made up of four plane surfaces Ha, II b, etc., therefore the carriage may be displaced transversely with respect to either pair (29-23, 2I-22) of diametrically opposed plungers when the carriage is subject to a change in the force :applied by the other air. When the rod is engaged by the latch 11, the carriage, and hence ithE'IOd, may be moved along the axis of the rod by turning the control knobs 25 and 2'! through aequal degrees of rotation either simultaneously or sequentially. Movement of the carriage and hence of the rod 8 and its specimen holder 88, at a right angle to the direction of the axis of the rod is accomplished by advancing one of the plungers 22 or 23 while withdrawing the other plunger an equal distance. Movement of the said parts in a direction other than at a right angle with respect to the axis of the rod is accomplished by moving one of the knobs 26 or 21 through a different are than the other. Ordinarily, none of these movements need comprise an excursion of more than, say, one-eighth of an inch, and such limited degrees of movement are easily achieved without danger of breaking the vacuum, by reason of the flexible nature of the elastic bushing 13 which surrounds the rod 8.

From the foregoing it will be apparent that the present invention provides an improved specimen stage for electron optical instruments, and one possessing the simplicity and vacuum-retaining features characteristic of rod-type specimen holders and, also, the high resolution, high magnification, and flexibility'heretofore achieved only with electronoptical instruments containing an evacuable auxiliary chamber or airlock.

What is claimed is:

1. An electron-optical instrument comprising an evacuable casing having a bore .in a'wall thereof, a rod-like specimen holder extending into said casing through said bore, said bore being of a diameter substantially greater than that of said rod and containing a. flexible vacuumtight bushing through which said rod extends, whereby said rod'may be subjected to axial'movement and to pivotal-movement about the center of said flexible bushing, a carriage mounted for movement in all directions in a common plane within said casing and upon which said specimen holder is supported in a plane parallel to said first mentioned plane, and means operatively connected to said carriage and'extending to the exterior of said casing for moving said carriage in its plane "to a position whereat said specimen holder is in a desired position in said parallel plane.

2. The invention as set forth in claim 1 and wherein said rod-like specimen holder is mounted for axial movement on and with respect to said carriage, and wherein said carriage and said specimen-holder are provided with complementary latch elements for securing said specimen holder upon movement of said holder to a predetermined position on said carriage.

3. In an electron-optical instrument comprising an evacuable casing having an axis along which electrons travel in the form of a "beam from a source to a target, a support mounted within said casing formovement in all directions in a plane normal to said axis, a rod-like specimen holder mounted upon said support for longitudinal movement along a line parallel to said plane and extendingto the exterior of said casing, and a plurality of actuating members operatively connected to said support and extending to .the exterior of said casing for moving said support and hence said specimen holder with respect to said electron beam.

4. In an electron-optical instrument comprising an evacuable casing having an axis along which electrons travel in the form of a beam from a source-to a target, a support mounted within said casing for movement in all directions in a plane normal to said axis, a flexible bushing in a wall "of said casing, a rod-like specimen holder,

having a specimen holding aperture therein, extending through said bushing and mounted for movement upon, and with respect to, said support, complementary latch and catch members upon said specimen-holder in a position to halt longitudinal movement of said specimen holder with respect to said support when the specimenholding aperture in said holder falls on a line which intersects said electron axis in said plane, and means operatively connected to said support and extending to the exterior of said casing for moving said support and hence said rod-like specimen holder along said line to a point whereat said specimen-holding aperture intersects said electron axis.

5. In an electron optical instrument comprising an evacuable casing having an axis along which electrons travel in the form of a beam from a source to a target, a flexible bushing in a wall of said casing, a rod-like specimen holder, having a specimen-holding aperture therein, extending through said bushing and supported therein for longitudinal movement and for pivotal movement about the center of said bushing, a support mounted within said casing for movement in all REFERENCES CITED The following references are of record in tho file of this patent:

UNITED STATES PATENTS Number Name Date 2,220,973 Marton Nov. 12, 1940 2,264,210 Krause Nov. 25, 1941 2,275,234 Ruedy Mar. 3, 1942 2,443,021 Bensen June 8, 1948 2,464,382 Dornfeld Mar. 15, 1949 2,467,224 Picard Apr. 12, 1949 

